Dublin (and Ireland in general) is a wonderful destination. you will defiantely enjoy it. if you enjoy medieval history or art, be sure to visit the Trinity College Library and see the Book of Kells and other illuminated manuscripts -- amazing. How old is your son? If he is underage in the U.S., but reasonably "old" (late teens), he might very well enjoy a visit to a pub. Even if he does not drink, the atmosphere is quite interesting and fun.

To me, few things are as fun as sitting in a pub in Dublin listening to traditional Irish music.